In a Long Term Evolution-Advanced (LTE-Advanced) standard-based wireless relay technology proposed by the 3rd Generation Partnership Project (3GPP) standard organization, a Relay Node (RN) provides a function and service similar to those of an ordinary Evolved Node B (eNB) for User Equipment (UE) accessing a cell of the RN, and also accesses a serving eNB (also called a Donor eNB (DeNB)) like ordinary UE through a wireless interface. Along with the large-scale construction and operation of high-speed railways, requirements on communication on trains continuously increase. However, it is difficult to meet a communication quality requirement of the high-speed railways under the coverage of an existing network eNB due to influence of Doppler frequency shift, frequent cell handover, great high-speed railway compartment penetration loss and the like on high-speed moving trains. Consequently, the deployment of RNs on high-speed railways is proposed in the industry, and such RNs are usually called mobile relays. FIG. 1 is an architecture diagram of a mobile relay system supporting a LIPA function in a high-speed railway scenario, and as shown in FIG. 1, users (UE1 and UE2) in a high-speed train can communicate with a relatively static MRN by virtue of a mobile relay technology, and in a moving process of the high-speed train, the MRN can be handed over between different DeNBs, thereby avoiding simultaneous handover of a great number of users in the high-speed train and ensuring quality of communication between the UE and the MRN. In addition, enhancing a backbone connection between the MRN and the DeNB may better improve the quality of communication between the users in the high-speed train. There is a LIPA Gateway (GW) arranged in an MRN shown in FIG. 1.
A mobile relay may adopt an architecture shown in FIG. 2 (the architecture the same as a standardized R10 fix relay, usually called architecture 2), and then a Serving Gateway (S-GW), Packet Data Network Gateway (P-GW) and relay GW of an MRN are located in the DeNB (called an initial DeNB) to which MRN initially accesses. The relay GW in the DeNB provides a proxy function for data and signaling of an S1 interface and an X2 interface. In such an architecture, when the MRN moves far away from the initial DeNB, data of UE arrives at the initial DeNB and then is routed to the serving DeNB, which causes a longer path and a longer delay. As a consequence, it is necessary to consider about a route optimization scheme, and when the MRN moves far away from the initial DeNB, the GW of the MRN is changed into a built-in GW of a DeNB serving the MRN. As shown in FIG. 3, if before the handover of the MRN, its GW (GW1) is located in DeNB1 while it is DeNB3 currently providing service for the MRN, then the data of the UE arrives at the GW of DeNB1 and then is routed to DeNB3 through DeNB2, which undoubtedly causes the prolonging of a data routing path. The MRN may relocate its GW to a built-in GW (GW4) of DeNB4 in a process of handover, for example, handover from DeNB3 to DeNB4, so that the data of the UE can directly arrive at DeNB4, the path is shortened, and the data delay is reduced.
In addition, in order to better meet a requirement of a user and further improve a user experience, 3GPP takes a LIPA supporting function of a mobile relay into consideration to provide a high-speed local service for UE of an LTE system and save a bandwidth resource of a backhaul link of an air interface. For example, the UE can be connected with a local Packet Data Network (PDN) to acquire a multimedia resource through a Line Gateway (LGW) combined with the MRN, or support a multiuser social network application such as file sharing, chatting and games through a local server. As shown in FIG. 1, an LGW function entity can be arranged in an MRN in a carriage. The LGW is connected with the PDN through a Security Gateway Interface (SGi). For connected-state UE with a LIPA connection, a direct tunnel for LIPA service data exists between the LGW and the MRN, and moreover, an S5 interface core network tunnel is established between the LGW in the MRN and the SGW of the UE for paging of IDLE-state UE and for S5 signaling transmission. After UE with a LIPA PDN connection enters an IDLE state, its direct tunnel is released, and the core network tunnel is reserved.
Under the condition that the mobile relay supports LIPA, the MRN is disconnected from an S-GW network element. Moreover, because the LGW and the MRN are combined into a whole, all data which is sent to the LGW combined with the MRN by a network element of a core network can arrive only after subjected to the routing of an RN P-GW combined with the DeNB. Consequently, the RN P-GW is required to allocate an IP address to the LGW, and the LGW may use an IP address the same as or different from that of the MRN. If handover occurs and the GW serving the MRN is relocated in a movement process of the MRN, a new PGW serving the MRN is required to allocate a new IP address to the LGW, that is, the address of the LGW may be changed.
An existing protocol specification does not support mobility of a LIPA PDN connection. In a Home Evolved Node B (HeNB) application scenario, if UE initiates Tracking Area Update (TAU), a source Mobility management unit (MME) serving the UE needs to check whether a LIPA PDN connection exists or not, and if the LIPA PDN connection exists, an Evolved Packet System (EPS) bearer context of the source MME in a TAU process does not contain a LIPA bearer, and a PDN disconnection process requested by the MME is executed to release a core network resource of the LIPA PDN connection. If the UE initiates a service request process and has the LIPA PDN connection, the MME needs to judge whether a cell where the UE is currently located is connected with the LGW with which the UE establishes the LIPA PDN connection according to the address of the LGW. If the cell is not connected with the LGW, the MME does not request for bearer establishment of the LIPA PDN connection, and executes a LIPA PDN releasing process, or the MME denies the service request and detaches the UE.
In a high-speed railway scenario, the MRN supports a LIPA function, and if UE does not move relative to the MRN and is still served by the same MRN and LGW, its LIPA PDN connection is not required to be released in TAU and service request processes of the UE. According to the existing protocol specification, once the UE with a LIPA connection initiates TAU, the MME releases its LIPA PDN connection. Moreover, if the GW is relocated after DeNB handover of the MRN, the address of the LGW combined with the MRN may be changed, and if the address of the LGW has been changed relative to the address in the last connected state when the IDLE-state UE initiates a service request, the LIPA PDN connection of the UE is released, the service request is even denied and the UE is detached. As a consequence, the abovementioned LIPA connection releasing problem needs to be solved in a scenario where the mobile relay supports LIPA.
Unfortunately, there is no related art for reference at present.